Nato chief Anders Fogh Rasmussen said: 'We will have more planes in the air, more ships on the water, and more readiness on the land.' Photograph: Georges Gobet/AFP/Getty Images

Nato has announced it is stepping up its presence around Russian borders to reassure eastern European member states, in an effort also aimed at increasing pressure on Moscow before international talks on the Ukrainian crisis on Thursday in Geneva.

The EU and the US intend to tighten sanctions against Moscow after the four-party negotiations – involving foreign ministers from Russia, Ukraine and the US and the EU foreign policy chief, Catherine Ashton – if Moscow does not stop what the west allege is the deliberating stoking of tensions in eastern Ukraine.

A spokesperson for the US secretary of state, John Kerry, said his primary goal was to persuade Moscow to halt its destabilising activities in eastern Ukraine, and call publicly for separatist groups to disarm and stand down.

Late on Wednesday the US president, Barack Obama, warned of unspecified "consequences" if Russia did not change course. "Each time Russia takes these kinds of steps that are designed to destabilise Ukraine and violate their sovereignty, there are going to be consequences," Obama told CBS News.

Pro-Russian separatists seized six armoured personnel carriers from the Ukrainian army on Wednesday, which they then drove in a victory lap through the centre of two towns held by militia units. Protesters seeking independence from Kiev have occupied at least nine government buildings in the region for more than a week – but this is the first time that separatist forces deep inside Ukraine have managed to seize heavy military equipment, and a further sign that the situation in the east is slipping out of Kiev's grip.

The reinforcements on Nato's eastern flank will take the form of more air patrols over the Baltic states, greater numbers of warships in both the Baltic and eastern Mediterranean, and more troops deployed in eastern Europe.

"Today, we agreed on a package of further military measures to reinforce our collective defence and demonstrate the strength of Allied solidarity," the Nato secretary general, Anders Fogh Rasmussen, said after a meeting of alliance members. "We will have more planes in the air, more ships on the water, and more readiness on the land. For example, air policing aircraft will fly more sorties over the Baltic region. Allied ships will deploy to the Baltic Sea, the eastern Mediterranean and elsewhere, as required."

"Military staff from Allied nations will deploy to enhance our preparedness, training and exercises. Our defence plans will be reviewed and reinforced. We will start to implement these measures straight away. More will follow, if needed, in the weeks and months to come."

The US, which is currently leading the air policing over the Baltic region, reinforced its presence on 20 March, increasing the number of F15 fighter jets based in Lithuania from four to 10. On 1 May, the Poles will take over leadership of the role, sending four Mig-29 jets, which will be augmented by four British Typhoons and up to 10 Danish F16 warplanes. French jets could meanwhile deploy to Poland to bolster patrols there.

The Nato buildup will also involve the redeployment of warships, some of them now participating in counter-piracy operations off Somalia, to the Baltic and the Mediterranean. A Nato official said the details of the naval measures were still being discussed.

The Nato commander in Europe, General Philip Breedlove, said several Nato member states had offered ground troops for deployment in eastern European member states and that he would be soon making recommendations on how they should be positioned. Breedlove said that the situation represented more than a crisis, adding: "For Nato, it's bigger than that. It's a paradigm shift."

However, the general added that he saw no evidence of a strategic Russian buildup on Ukraine's borders. He stressed the military movements were intended entirely to reassure Nato members along Russia's borders who had been unnerved by Russian actions in Ukraine.

The air force general said he had attempted to call the Russian chief of general staff, Valery Gerasimov, to explain that the deployments were entirely defensive but had not been able to reach him.

Meanwhile, EU officials in Brussels said the list of Russians subject to visa bans and asset freezes would be expanded by the end of the week. The US state department also signalled it would co-ordinate a further tightening of sanctions with its European partners, but not before the Geneva talks.

"Don't expect any before tomorrow's meetings," Marie Harf, deputy spokesperson at the state department, said. "But if there are not steps taken by Russia to de-escalate, we will take additional steps, including additional sanctions."

The negotiations will bring together Kerry, his Russian counterpart, Sergei Lavrov, the Ukrainian foreign minister, Andrii Deshchytsia, and the EU's Ashton. It will mark the first time the quartet has met since the Ukrainian crisis erupted in February.

In addition to one four-way encounter, Kerry will conduct separate bilateral meetings with Lavrov, Deshchytsia and Ashton. Western officials, however, cautioned that the talks were unlikely to bring a diplomatic breakthrough.

Harf said that "top of the list" of US demands would be that Russia halt what the US alleges are destabilising activities in eastern Ukraine. The US wants Russia to publicly call on separatists exerting control in cities in eastern Ukraine to disarm and stand down.

The US also wants Russia to pull its estimated 40,000 troops away from the Ukrainian border and withdraw from Crimea, the Ukrainian region Moscow has in effect annexed.